Citrus black rot

Citrus black rot is a fungal infection caused by the pathogen Alternaria citri. This disease primarily impacts the fruit of citrus species, leading to internal decay and significant post-harvest losses, which makes it a major concern for citrus fruit producers globally.

The disease affects various citrus cultivars, most notably lemons, oranges, and mandarins. While the primary damage is often hidden within the fruit, the pathogen can also infect leaves and twigs, leading to defoliation and a general weakening of the tree's physiological health.

Symptoms of the infection include the appearance of dark, sunken lesions on the peel, often near the stem end. As the fungus progresses, the internal tissue turns black and turns into a soft, dry rot. If observed closely under high humidity, one may see a dark, olive-colored fungal mycelium and spore mass on the fruit surface.

The development of Alternaria citri is strongly correlated with warm, humid weather, particularly during the fruit ripening stage. The fungus exploits entry points on the fruit, such as minor skin abrasions, growth cracks, or wounds inflicted by pests like citrus rust mites, enabling it to colonize the interior tissue rapidly.

Effective management and prevention strategies include several critical agronomic practices:

• Maintaining tree vigor through proper fertilization and irrigation to prevent stress.
• Applying preventive copper-based or systemic fungicides during vulnerable growth stages.
• Controlling insect populations, particularly those that pierce the fruit rind.
• Ensuring proper sanitation in the orchard by removing diseased fruit and plant debris.
• Harvesting fruit carefully to avoid injuries that allow fungal entry during storage.